Double unit microwave oven having an energy seal therebetween

ABSTRACT

A microwave oven consisting of two structural units, the first structural unit comprising the electrical components, including the magnetron, and the second unit comprising, inter alia the oven cavity. A quarter wave choke is formed at the area where both units are joined.

1451 June 25, 1974 DOUBLE UNIT MICROWAVE OVEN HAVING AN ENERGY SEAL THEREBETWEEN Inventors: Helge Frithiof Wallin, Norrkoping;

Leo Malmquist, Ektorp, both of Sweden Assignee: U.S. Philips Corporation, New

. York, NY.

Filed: Dec. 16, 1971 Appl. No; 208,599

Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 3,182,164 5/1965 lronfield 219/1055 3,497,656 2/1970 Staats et a1. 219/1055 3,531,613 9/1970 Domenichini et a1. 219/1055 3,576,417 4/1971 Tingley 219/1055 Primary ExaminerJ. V. Truhe Assistant Examiner-Hugh D. Jaeger Attorney, Agent, or FirmFrank R. Trifari; Bernard Franzblau 5 7] ABSTRACT A microwave oven consisting of two structural units, the first structural unit comprising the electrical com- Dec. 21, 1970 Sweden 17333/70 ponems, including the magnetron, and the second unit comprising, inter alia the oven cavity. A quarter wave choke is formed at the area where both units are Field of Search 219/1055 lowed- 10 Claims, 4 Drawing Figures uril 25 W16 E-23 12 2 I \22 l1'- 13 43 Ill Pmminwm 1914 18191899 sum 1 n; 4

INVENTOR5 HELGE F. WALLIN By LEO MALMQUIS'I AGEN DOUBLE UNIT MICROWAVE OVEN HAVING AN ENERGY SEAL THEREBETWEEN The present invention relates to a microwave oven comprising a magnetron which is included in an electrical supply circuit and an oven cavity which is connected to the magnetron via a wave guide for feeding microwave energy.

The invention has for its object to provide a construction for such an oven which can be inexpensively manufactured and which can be readily repaired and serviced.

To this end the invention is characterized in that the magnetron constitutes, together with its electrical supply circuit, a first structural unit in which the said components are accommodated in a common housing. An antenna of the magnetron projects from one wall of the housing. The first structural unit is combined with a second structural unit comprising the oven cavity. The second unit includes plates projecting therefrom and enveloping a space for accommodating the housing. The housing has a position in this space such that the wall of the housing from which the antenna projects is situated adjacent to and confronting one wall of the oven cavity but at some distance from and opposite to the one wall of the oven cavity so that at least a portion of the said wave guide is formed 'by the space between the said oppositely arranged walls. In addition at the area where the housing and the plates are joined a cavity is provided which is formed as a quarter wave choke and which extends along the entire circumference of the housing so as to prevent radiation of microwave energy from the wave guide. The housing preferably has the shape of a container having a lid to which the magnetron is secured, said container being situated directly below the oven cavity, the space between the lid and the bottom of the oven cavity forming at least a portion of the waveguide for feeding microwave energy to the oven cavity. The cavity which serves as a quarter wave choke can then be formed by a groove which is delimited by appropriately shaped portions of the lid and the container and which has a slit-shaped opening at the outside, said opening being closed by the plates projecting from the second unit.

With the exception of a small number of electrical provisions, such as oven illumination, a door switch and the like which are to be provided in or near the oven cavity and the oven door, all electrical components of a microwave oven constructed according to the invention are gathered in the said housing which can be separately manufactured and which can be assembled in a final assembly stage with the also separately manufactured second unit comprising the oven cavity.

Due to the use of the space between the oppositely arranged walls of both units as a wave guide for the energy supply to the oven cavity, and due to the use of a quarter wave choke at the area where the housing and the plates projecting from the second unit are joined, mounting and disassembling of the units is very simple as no separate sealing means need be provided at the joint.

Simple attachment means will suffice for fixing the housing in the correct position in the second unit, said position not being subject to very severe accuracy requirements. If the electrical unit is to be repaired, the entire unit may be replaced by a spare unit, if desired,

after which the replaced unit can be repaired in the factory.

In order that the invention may be readily carried into effect, one embodiment thereof will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIGS. la and lb are perspective views of a container and a lid, respectively, which together form a housing accommodating a magnetron and a supply circuit and constituting a first structural unit for a microwave oven according to the invention.

FIG. 2 is a perspective view of a second structural unit for the microwave oven according to the invention, consisting of an oven cavity, a wave guide system and projecting plates, and

FIG. 3 is a sectional view of the microwave oven after assembly of the two units shown in FIGS. 1 and 2.

In FIG. lathe reference numeral 10 denotes a watertight container having two successive projecting shoulders l1 and 12 at its upper side. FIG. lb shows a bowlshaped lid 13 which fits into the container 10 and which has a projecting shoulder 14 at its upper side which corresponds to the upper shoulder 12 of the container. The container 10 and the lid 13 together constitute a first structural unit for a microwave oven, said unit comprising virtually all electrical components of the oven, including the magnetron and its supply circuit. As is shown in FIG. lb, the magnetron 15 is secured to the lower side of the lid 13, its antenna 16 projecting through an aperture 17 in the centre of the lid.

The supply circuit for the magnetron comprises a high voltage transformer 18, capacitors l9 and a high voltage rectifier 20. As appears from FIG. Ia, these components are arranged in-the container such that they leave a space for the magnetron 15. The container furthermore houses a filament transformer (not shown) and preferably also a switching element in the form of a variable thyristor or a socalled triac for switching on and off the magnetron l5, and any other electrical components suitable for mounting in the container. In the front wall of the container a lead-through 21 is provided for connecting the interior of the container to the supply voltage and to any switching members mounted outside the container. All lead-throughs are grounded via a capacitor so as to prevent interference.

The container 10 can be filled with oil, paraffin or the like for cooling purposes. The lid is placed on the container, as shown in FIG. 3, after the magnetron 15 has been mounted against the lower side of the lid 13, the remaining electrical components have been arranged in the container 10 and all interconnections have been made. The dimensions of the lid 13 are such that its lower portion bears on the lower shoulder 11 of the container 10, thus closing the container. The lid 13 is preferably soldered to the shoulder 11 so that a watertight seal is obtained. As appears from FIG. 3, the container l0 and the lid 13 are further shaped such that a groove 22 remains between the second shoulder 12 of the container and the shoulder 14 of the lid, said groove extending along the entire circumference of the container and having a slit-shaped opening 23 at the outside.

FIG. 2 shows a second structural unit for the microwave oven comprising an oven cavity, a wave guide system and an outer envelope. The oven cavity 24 (see FIGS. 2 and 3) is defined by a bottom plate 25, an

upper wall 26 and side walls 27 and 28. The oven cavity 24 is situated within an outer envelope 30 consisting of an upper plate 31, side plates 32, 33 and a rear plate (not shown). Both side plates 32, 33 and the rear plate extend into plates 32', 33' which project downwards from the second unit, a space 36 being formed below the oven cavity for accommodating the housing l0, 13 shown in FIGS. la and lb.

As is shown in FIG. 3, the side walls 27, 28 of the oven cavity 24 are situated at some distance from the side plates 32, 33 of the outer envelope so that therebetween slit-shaped spaces 37, 38 are present. Likewise, the upper wall 26 of the oven cavity 24 is situated at some distance from the upper plate 31 of the outer envelope so that therebetween a space 39 exists which communicates with both side spaces 37, 38. As will be described hereinafter, these spaces outside the walls of the oven cavity form a portion of a wave guide system During the manufacture of the oven, first the electrical unit is produced in that the electrical components are mounted in the container and are electrically interconnected, after which the container is filled with oil or paraffin and is closed. The second structural unit, comprising the oven cavity and the wave guide system, is manufactured in a separate manufacturing process. The units are then combined in that the housing l0, 13 with the electrical components is placed in the space 36 below the oven cavity via recesses 41, 42 and is secured in the correct position by means of suitable fixing materials. When the housing is in this position, a space 43 exists between the lid 13 of the housing and the bottom 25 of the oven cavity, said space communicating with both side spaces 37, 38, thus completing the wave guide system. The magnetron antenna 16 which projects through the lid 13 transfers microwave energy to the wave guide system and this energy leaks into the oven cavity 24 through the slits 40.

The dimensions and the position of the housing l0, 13 below the oven cavity. 24 are such that the upper side of the housing closely adjoins the projecting plates of the outer envelope along three sides, the slitshaped opening 23 of the groove 22 being closed by these projecting plates. At the remaining front side of the housing a special strip (not visible in the drawing) projects downwards from the second unit, said strip closing the slit-shaped opening at the front of the housing so that the groove is closed along the entire circumference. The depth of the groove 22, taken from the slit-shaped opening to the bottom of the groove, i.e., the shoulder 12, is substantially equal to one quarter of the wavelength of the microwaves. The groove thus constitutes a so-called quarter wave choke for the microwave energy which otherwise tends to leak from the wave guide system between the outer envelope and the housing, so that this leakage is prevented. Due to the presence of this quarter wave choke along the entire circumference of the housing, this housing need not be in galvanic contact with the interior of the outer envelope. The housing l0, 13 may thus be secured in the space 36 so as to be readily detachable. After the slit-shaped opening 23 the leakage energy has to pass a second slit between the outer envelope and the oppositely situated portion of the housing, said slit also having a length of approximately one quarter wavelength, thus also contributing towards prevention of energy leakage.

What is claimed is:

l. A microwave oven comprising a first structural unit that includes a magnetron and its electrical supply circuit accommodated Within a common enclosed housing, an antenna of the magnetron projecting outwardly from one wall of the housing, means for combining said first structural unit with a second structural unit comprising wall means defining an oven cavity which includes a pair of plates projecting from said second unit so as to enclose a space for accommodating the housing of said first unit, said housing being positioned within said space such that the one wall of the housing from which the antenna projects is spaced apart from and adjacent to one wall of the oven cavity, a waveguide for coupling the microwave energy from the magnetron antenna to the oven cavity, at least a portion of said wave guide being formed by the space between the said oppositely arranged one walls of the housing and the oven cavity, means providing a cavity in the area where the housing and the plates are joined and which extends along the entire circumference of the housing, said cavity being dimensioned to form a quarter wave choke at the magnetron frequency thereby to prevent radiation of microwave energy from the wave guide.

2. A microwave oven as claimed in claim 1, characterized in that the housing has the shape of a container including a lid to which the magnetron is secured to extend within the container, said container being situated directly below the oven cavity, the space between the lid and the bottom of the oven cavity forming said portion of the wave guide for coupling microwave energy to the oven cavity.

3. A microwave oven as claimed in claim 2, characterized in that said quarter wave cavity is formed as a groove delimited by step shaped portions of the lid and the container and having a slit-shaped opening around the outside circumference, the plates projecting from the second unit so as to overlap said opening and close same.

4. A microwave oven as claimed in claim 1, characterized in that at least two other walls of the oven cavity are arranged in spaced relationship to at least two other walls of the second unit to form passageways that communicate with the space between said one wall of the oven cavity and said one wall of the housing so that a complete wave guide system for coupling microwave energy to the oven cavity is formed, at least the bottom and the upper wall of the oven cavity being provided with slits for allowing microwave energy to pass into the oven cavity.

5. A microwave oven comprising first and second structural units joined together to form said oven, said first unit comprising a housing for the oven electrical components and including a magnetron with an antenna projecting outwardly from one wall thereof, and said second unit comprises an oven heating cavity, a wave guide system for coupling microwave energy from the antenna to the oven cavity and an outer container for said cavity and wave guide system, at least two walls of said container extending therefrom so as to define a space for accomodating said housing of the first unit, said housing being mounted within said space with said one wall spaced apart from and adjacent to one wall of the oven cavity to define therewith a portion of said wave guide system, the walls of said outer container and said oven cavity being spaced apart to further define the waveguide system, said housing and container being shaped to form a gap in the area where they are joined together and dimensioned so as to form a quarter wave choke at the magnetron frequency, said gap extending about the periphery of the housing to prevent the escape of microwave energy between the housing and the container.

6. A microwave oven as claimed in claim 5 wherein said first structural unit comprises a boxlike housing open at one end and said one wall of the housing comprises a cover for the open end of the housing on which the magnetron is mounted with its antenna outwardly protruding therefrom.

7. A microwave oven as claimed in claim 5 wherein said first structural unit comprises a boxlike housing open at one end with the upper edges thereof extending laterally outward to define a step-like edge portion, and said one wall of the housing comprises a cover for said open end with an outwardly extending peripheral steplike edge portion arranged and dimensioned so as to fonn with the upper edge of the housing said quarter wave gap.

8. A microwave oven as claimed in claim 7 wherein the extending wall portions of said outer container overlap said quarter wave gap when said first and second units are joined together.

9. A microwave oven as claimed in claim 8 wherein said extending wall portions further overlap at least a portion of the side walls of the housing and are spaced therefrom so as to form a second gap so dimensioned as to form a second quarter wave choke at the magnetron frequency.

10. A microwave oven as claimed in claim 5 wherein said one wall of the oven cavity and a second oven cavity wall opposite to said one cavity wall contain openings therein to allow the microwave energy to pass into the oven cavity. 

1. A microwave oven comprising a first structural unit that includes a magnetron and its electrical supply circuit accommodated within a common enclosed housing, an antenna of the magnetron projecting outwardly from one wall of the housing, means for combining said first structural unit with a second structural unit comprising wall means defining an oven cavity which includes a pair of plates projecting from said second unit so as to enclose a space for accommodating the housing of said first unit, said housing being positioned within said space such that the one wall of the housing from which the antenna projects is spaced apart from and adjacent to one wall of the oven cavity, a waveguide fOr coupling the microwave energy from the magnetron antenna to the oven cavity, at least a portion of said wave guide being formed by the space between the said oppositely arranged one walls of the housing and the oven cavity, means providing a cavity in the area where the housing and the plates are joined and which extends along the entire circumference of the housing, said cavity being dimensioned to form a quarter wave choke at the magnetron frequency thereby to prevent radiation of microwave energy from the wave guide.
 2. A microwave oven as claimed in claim 1, characterized in that the housing has the shape of a container including a lid to which the magnetron is secured to extend within the container, said container being situated directly below the oven cavity, the space between the lid and the bottom of the oven cavity forming said portion of the wave guide for coupling microwave energy to the oven cavity.
 3. A microwave oven as claimed in claim 2, characterized in that said quarter wave cavity is formed as a groove delimited by step shaped portions of the lid and the container and having a slit-shaped opening around the outside circumference, the plates projecting from the second unit so as to overlap said opening and close same.
 4. A microwave oven as claimed in claim 1, characterized in that at least two other walls of the oven cavity are arranged in spaced relationship to at least two other walls of the second unit to form passageways that communicate with the space between said one wall of the oven cavity and said one wall of the housing so that a complete wave guide system for coupling microwave energy to the oven cavity is formed, at least the bottom and the upper wall of the oven cavity being provided with slits for allowing microwave energy to pass into the oven cavity.
 5. A microwave oven comprising first and second structural units joined together to form said oven, said first unit comprising a housing for the oven electrical components and including a magnetron with an antenna projecting outwardly from one wall thereof, and said second unit comprises an oven heating cavity, a wave guide system for coupling microwave energy from the antenna to the oven cavity and an outer container for said cavity and wave guide system, at least two walls of said container extending therefrom so as to define a space for accomodating said housing of the first unit, said housing being mounted within said space with said one wall spaced apart from and adjacent to one wall of the oven cavity to define therewith a portion of said wave guide system, the walls of said outer container and said oven cavity being spaced apart to further define the waveguide system, said housing and container being shaped to form a gap in the area where they are joined together and dimensioned so as to form a quarter wave choke at the magnetron frequency, said gap extending about the periphery of the housing to prevent the escape of microwave energy between the housing and the container.
 6. A microwave oven as claimed in claim 5 wherein said first structural unit comprises a boxlike housing open at one end and said one wall of the housing comprises a cover for the open end of the housing on which the magnetron is mounted with its antenna outwardly protruding therefrom.
 7. A microwave oven as claimed in claim 5 wherein said first structural unit comprises a boxlike housing open at one end with the upper edges thereof extending laterally outward to define a step-like edge portion, and said one wall of the housing comprises a cover for said open end with an outwardly extending peripheral step-like edge portion arranged and dimensioned so as to form with the upper edge of the housing said quarter wave gap.
 8. A microwave oven as claimed in claim 7 wherein the extending wall portions of said outer container overlap said quarter wave gap when said first and second units are joined together.
 9. A microwave oven as claimed in claim 8 wherein said extending wall portions further overlap at least a portion of the side walls of the housing and are spaced therefrom so as to form a second gap so dimensioned as to form a second quarter wave choke at the magnetron frequency.
 10. A microwave oven as claimed in claim 5 wherein said one wall of the oven cavity and a second oven cavity wall opposite to said one cavity wall contain openings therein to allow the microwave energy to pass into the oven cavity. 